Allow eager loading rules

To eager load rules, reuse the association without scope.
Filter those rules using `regular?` method.

ee/app/controllers/concerns/ee/issuable_collections.rb

@@ -9,7 +9,7 @@ module EE
     def preload_for_collection
       @preload_for_collection ||= case collection_type
                                   when 'MergeRequest'
-                                    super.push(:approvals)
+                                    super.push(:approvals, :approval_rules)
                                   else
                                     super
                                   end

ee/app/models/approval_merge_request_rule.rb

@@ -39,4 +39,9 @@ class ApprovalMergeRequestRule < ApplicationRecord
 
     self.approved_approver_ids = merge_request.approvals.map(&:user_id) & approvers.map(&:id)
   end
+
+  def regular
+    !code_owner?
+  end
+  alias_method :regular?, :regular
 end

ee/app/models/approval_project_rule.rb

@@ -9,6 +9,11 @@ class ApprovalProjectRule < ApplicationRecord
   scope :regular, -> { all }
   scope :code_owner, -> { none }
 
+  def regular
+    true
+  end
+  alias_method :regular?, :regular
+
   def code_owner
     false
   end

ee/app/models/approval_state.rb

@@ -36,7 +36,7 @@ class ApprovalState
   end
 
   def approval_rules_overwritten?
-    merge_request.approval_rules.regular.exists?
+    merge_request.approval_rules.any?(&:regular?)
   end
   alias_method :approvers_overwritten?, :approval_rules_overwritten?
 
@@ -135,10 +135,10 @@ class ApprovalState
   def regular_rules
     strong_memoize(:regular_rules) do
       rule_source = approval_rules_overwritten? ? merge_request : project
-      rules = rule_source.approval_rules.regular
+      rules = rule_source.approval_rules.select(&:regular?)
 
       unless project.feature_available?(:multiple_approval_rules)
-        rules = rules.order(id: :asc).limit(1)
+        rules = rules[0, 1]
       end
 
       wrap_rules(rules)
@@ -147,7 +147,7 @@ class ApprovalState
 
   def code_owner_rules
     strong_memoize(:code_owner_rules) do
-      wrap_rules(merge_request.approval_rules.code_owner)
+      wrap_rules(merge_request.approval_rules.select(&:code_owner?))
     end
   end
 

ee/spec/models/approval_merge_request_rule_spec.rb

@@ -14,6 +14,22 @@ describe ApprovalMergeRequestRule do
     end
   end
 
+  describe '#regular' do
+    it 'returns true for regular records' do
+      subject = create(:approval_merge_request_rule, merge_request: merge_request)
+
+      expect(subject.regular).to eq(true)
+      expect(subject.regular?).to eq(true)
+    end
+
+    it 'returns false for code owner records' do
+      subject = create(:approval_merge_request_rule, merge_request: merge_request, code_owner: true)
+
+      expect(subject.regular).to eq(false)
+      expect(subject.regular?).to eq(false)
+    end
+  end
+
   describe '#approvers' do
     before do
       create(:group) do |group|

ee/spec/models/approval_project_rule_spec.rb

@@ -21,6 +21,13 @@ describe ApprovalProjectRule do
     end
   end
 
+  describe '#regular' do
+    it 'returns true' do
+      expect(subject.regular).to eq(true)
+      expect(subject.regular?).to eq(true)
+    end
+  end
+
   describe '#code_owner' do
     it 'returns false' do
       expect(subject.code_owner).to eq(false)